The present invention relates to an end plate arranged on an end of a cell stack of a fuel cell in a direction in which cells are stacked.
An end plate of a fuel cell includes a plate body and fastening portions. The plate body has the form of a rectangular plate that includes two long sides and two short sides. The fastening portions are located on the edges of the plate body. The fastening portions are fastened to a case that contains a cell stack of the fuel cell. When the fastening portions of the plate body are fastened to the case, the plate body (end plate) presses the cell stack in the direction in which cells are stacked and keeps the cells stacked. When pressing the cell stack as described above, the end plate receives a reaction force from the cell stack.
There is a demand for a method that manufactures the end plate with high productivity. To meet the demand, a die casting process may be employed to charge molten metal under high pressure into a mold. In such a die casting process, the molten metal is charged into the mold almost at the same time as when gas is completely discharged from the mold. This may form voids (hollow portions) in the manufactured end plate if the manufactured end plate is thick.
As described in Japanese Laid-Open Patent Publication No. 2015-95321 and Japanese Patent No. 5313548, thickness-reducing recesses and reinforcement ribs may be arranged at a portion of the plate body surrounded by the fastening portions to reduce the thickness of the end plate while obtaining the strength required for the end plate. The recesses are formed by removing material in the thickness-wise direction from the plate body. The formation of the recesses in the plate body forms the ribs between adjacent ones of the recesses. The recesses and ribs of the plate body reduce the thickness of the end plate while obtaining the strength required for the end plate.
In Japanese Patent Publication No. 2015-95321, the recesses have triangular or quadrilateral cross-sections in a plan view and are irregularly arranged. Thus, the ribs formed between adjacent ones of the recesses extend in different directions. In Japanese Patent No. 5313548, the recesses have quadrilateral cross-sections in a plan view and are regularly arranged parallel to the short sides and the long sides of the plate body. The ribs formed between adjacent ones of the recesses extend parallel to the long sides and the short sides of the plate body. Thus, the ribs are arranged in a grid-like manner.
When fastening the fastening portions of the plate body to the case, the end plate presses the cell stack to keep the cells stacked. Thus, the end plate receives reaction force from the cell stack, and stress resulting from the reaction force acts on the end plate.
When employing recesses and ribs such as those of Japanese Laid-Open Patent Publication No. 2015-95321, the ribs will extend in different directions. Thus, when stress resulting from the cell stack acts on the end plate, the amount of stress acting on the ribs will differ between ribs. In such a case, stress will be concentrated on a rib that is arranged at a certain location. When stress is concentrated on a rib arranged at a certain location, the durability at such a location may be adversely affected.
When employing recesses and ribs such as those of Japanese Patent Publication No. 5313548, the ribs extending parallel to the long sides and short sides of the plate body will be arranged in a grid-like manner. In this case, when the end plate receives reaction force from the cell stage and stress acts on the end plate, a small stress acts on the ribs extending parallel to the long sides, while a large stress acts on the ribs extending parallel to the short sides. The factors causing stress to act in such a manner will now be described.
The two ends of each rib that extend parallel to the longs sides of the plate body are located in the proximity of the fastening portions of the plate body. Further, the distance is long between the two ends of such a rib. Thus, the ribs extending parallel to the long sides easily deform when receiving a reaction force. This decreases the stress acting on such ribs resulting from the reaction force. The two ends of each rib that extend parallel to the short sides of the plate body are also located in the proximity of the fastening portions of the plate body. However, the distance is short between the two ends of such a rib. Thus, the ribs extending parallel to the short sides resist deformation when receiving a reaction force. This increases the stress acting on such ribs resulting from the reaction force.
Accordingly, when employing recesses and ribs such as those of Japanese Patent Publication No. 5313548, stress is easily concentrated at certain locations in the ribs extending parallel to the short sides. This may adversely affect the durability at such locations.